1. Field of the Invention
The present invention relates to antennas, and in particular relates to phased array antennas useful for radar applications.
2. Description of the Prior Art
A basic analysis of phased array antenna technology is given by S. A. Schelkunoff, in the treastise Electromagnetic Waves, D. Van Nostrand Company, Inc., New York, 1943; and in an article entitled "A Mathematical Theory of Arrays" appearing in the January 1943 issue of the Bell System Technical Journal. Prior art phased array radar antennas have heretofore been used exclusively for governmental applications. There are a number of reasons for this, but primarily the failure to utiilize phased array radar antennas in civilian airport surveillance radars and on-board aircraft radars stems from cost factors.
The high cost of military phased array radar systems are traceable to the time requirements for such systems, which must be capable of intercepting and tracking ultra-high performance aircraft and missiles. Accordingly, such military systems have heretofore utilized high speed electronic components to achieve phase tuning within the individual wave guide elements, which means the acceptance of poor phase shifting paramters (for example, an incremental phase shift of 22.5 degrees is typical for state of the art military systems). To compensate for this problem, such military systems employ large numbers of wave guide elements, on the order of several thousand. As a result, by employing electronic tuning in each waveguide element, the cost for such a system goes well beyond the capabilities of a municipal airport facility; further, it is clear that such systems are quite large and are incapable of being employed on board single engined private aircraft.
A number of prior art patents disclosed various phased array radar antenna and related techniques. For example, Rearwin, in U. S. Pat. No. 2,967,301 teaches a selective directional slotted waveguide antenna. Mohr et al, in U.S. Pat. 3,736,535 teach a phase shift antenna for discriminating radar echoes from noise. This system employs ferrite shifters for providing phase shift in a circular polarization mode. U.S. Pat. No. 3,775,796 to Heeren et al suggests the use of a parasitic reflector in conjunction with an array of radiating elements smaller than the reflector, such that the shape of the reflector is utilized to determine beam width and direction. Blass, in U.S. Pat. No. 3,408,653, teaches a phased array antenna utilizing feed members spaced outside the focal plane and controlled to produce feed points within the focal plane of the impinging surface of the antenna. Various other phased array and related microwave processing techniques are disclosed in the following U.S. Pat. Nos.: 3,706,998 to Hatcher et al; 3,534,365 to Korvin et al; 3,803,619 to Meek et al; 3,404,405 to Young; 3,276,023 to Dorne et al; 2,530,580 to Lindenblad; and 3,761,943 to Harper et al.
While all of the above references disclose various techniques for solving the sophisticated problems associated with large and complex military phased array systems, this technology adds to the overall costs of such systems. Further, prior art phased array radar antennas require specially designed electronic systems which cannot be suitably employed with conventional radar antennas, and vice versa.